Tolterodine is a new muscarinic receptor antagonist designed for the treatment of urge incontinence, also called detrusor instability (DI). It has a more tolerable side effect profile of dry mouth and swallowing difficulties than previously used drugs. It was approved by FDA on March 25, 1998. This study aims to determine the percentage of patients with DI who require dose escalation or reduction when the initial dose is 1mg; and to evaluate clinical improvement in symptoms of urgency, frequency and incontinence when the dose is increased to 2mg. The initial study (Part A) is a single-blind, multi-center study which lasts four months. Subjects who wish to continue may enter an open label extension (Part B) for eight more months. Data is collected by patient interviews and urinary bladder diaries.